1. Field of the Invention
The invention relates generally to wireless communication and more particularly to systems and methods for digital call processing.
2. Background
Cellular wireless communication devices and networks are increasingly providing more and more services to users. Some services, such as two-way voice calls, can commonly be performed using either a digital or an analog network. Other services typically require a digital network, and cannot be performed with an analog network. One such service is push to talk (PTT) communications. In PTT communications, a user can instantly connect to another wireless communication device, instead of having to wait for the other device to ring and for the other user to answer the call. With a single push of a button the PTT call is connected.
PTT calls are commonly half duplex calls. Half duplex means that only one person can speak at a time. Unlike traditional full duplex calls, both parties cannot speak simultaneously. Of course, speech is not the only possible data carried on a PTT or traditional full duplex call. Speech is just considered here as the data for illustrative purposes. Other types of audio communication in addition to text and picture or video may also be possible.
To accomplish the instantaneous connection capability, a network must maintain presence information for each PTT enabled wireless communication device. For example, if A and B are users of PTT enabled wireless communication devices C and D, respectively, then the network must keep track of devices C and D so that C can connect instantly to device D. Additionally, A can cause his or her device C to be available for instant connection with device D or not to be available.
Not only does the network maintain information about the devices C and D, but each of the devices also commonly receives the information about the presence of other devices. For example, A can set the state of device C to receive PTT calls or not receive PTT calls. If device C is in a state of receiving PTT calls, and A wants to stop receiving PTT calls, A can select an option in the menu on his or her device C to stop receiving calls. Conversely, if device C is in a state of not receiving PTT calls, and A wants to start being available to receive PTT calls, A can select another option in the menu on his or her device C to start being available to receive PTT calls. To change states like this, the device C must send a message to the network indicating that the state is to be changed. The network must send a similar message to all devices such as device D that are configured to make PTT calls to device C. Such messages from the device changing state, such as device C, and to the other devices, such as device D, that need to know about the change of state are called presence messages.
PTT presence messages are typically sent on digital networks only. Thus, even though a wireless communication device might be configured to communicate on digital and analog networks, it may be necessary to restrict the device to digital networks only in order to send a presence message. Restricting the device to digital networks only is called restricting to digital mode only, or entering digital only mode.
After the PTT presence message is sent, the restriction to digital only mode can be removed so that the wireless communication device can again possibly communicate in either digital or analog mode.
Moving in and out of digital only mode is accomplished by using a preferred roaming list (PRL). A PRL is stored in the memory of the wireless communication device. The PRL contains records of all of the wireless communication systems or networks that the wireless communication device can communicate with. Several examples of using PRL's are described in U.S. Pat. No. 5,995,829, issued Nov. 30, 1999; U.S. Pat. No. 6,415,148 B1 (hereinafter, “the '148 patent”), issued Jul. 2, 2002; U.S. Pat. No. 6,466,802 B1 issued Oct. 15, 2002; U.S. patent application No. 2003/0134637 A1 published Jul. 17, 2003; U.S. patent application No. 2004/0110503, published Jun. 10, 2004; and U.S. patent application No. 2004/0121781 A1, published Jun. 24, 2004, which are each hereby incorporated in whole herein by reference.
As described in the '148 patent, the PRL typically contains a complete list of possible systems that the wireless communication device may encounter. The PRL contains preference information regarding each of the systems. Preference information means indications of which systems, networks and channels are preferred. Specifically, preference information may be information regarding system, network, channel, mode (e.g., digital or analog), geographical information. That is, preference information is any information on which a preference can be made by a wireless communication device. Preferences are selections based on preference information. For example, a wireless communication might be in a digital only mode. The digital only mode means that a preference is selected. Only those systems and networks having a digital indication in the preference information in the PRL can be used by the wireless communication device.
FIG. 5 is a flow chart illustrating a typical algorithm involving system acquisition. In step 500, the algorithm starts. The start step 500 may be powering up of the wireless communication device. In step 505, an ordered set of channels is derived from the PRL 510 and any preferences 515 (e.g., digital only). Specifically, an acquisition table 517 is contained in the PRL 510. The ordered set of channels is derived from the acquisition table 517, and is known as a scan list. In step 520 the ordered set of channels is sorted based on the most recent used list (MRU) 525. In step 530 the wireless communication device acquires a communication system. Once the communication system is acquired, the device knows its geographical location. In step 533, another set of ordered channels is derived based on any preferences 515 and the PRL 510. Specifically, system table geo information 536 is used to derive the set of ordered channels. The set of ordered channels derived this way is another scan list, which can be known as a rescan list.
Typically, subscribers, such as S1, subscribe to wireless communication services from a particular service provider, or network. For example, S1 may subscribe to service provider H1. S2 may also subscribe to service provider H1. Service provider H1 may have a relationship with service provider R1 so that subscribers of service provider H1, such as S1 and S2, can use service provider R1's network, for a fee paid by service provider H1 to service provider R1.
Service provider H1 may also have a relationship with service provider R2 so that subscribers of service provider H1 can use service provider R2's network, for a fee paid by service provider H1 to service provider R2. However, the fees paid to R2 may be more than the fees paid to R1. In that case, H1 may prefer that H1's subscribers, such as S1 and S2, use R1's network instead of R2's network, if possible. Of course, if possible, H1 prefers that subscribers, such as S1 and S2, use H1's network. The level, or order, of preference of networks is stored in the PRL.
Continuing the description of network preferences, service provider H1 might have a digital network and an analog network. H1 might prefer that subscribers use H1's digital network instead of H1's analog network whenever possible. As another example, H1 might not have any relationship with service provider N. Thus, H1's subscribers, such as S1 and S2, might not be allowed to place calls on network N. If network N is the only network available, then subscriber S1's device, say D1, and subscriber S2's device, say D2, may indicate that no service is available. Of course, in the case of calls placed to an emergency response service, H1's subscribers would be allowed to use network N.
Given the above examples, H1's digital network would be referred to as the most preferred network. N's network would not be allowed. The other networks would fall between the extremes of most preferred and not allowed. For example, R2's network might be the least preferred network, aside from the not allowed network N. H1's analog network might be more preferred than R2's network, but less preferred than R1's network. R1's network might be more preferred than H1's analog network but less preferred than H1's digital network.
The above arrangement of networks and preference relationships is actually a simple example. In reality, more networks are involved, and the PRL is complicated by several other factors as well. One such factor is geography. The PRL stores geographic information, known as “geo information”, or simply “geo”. The geo information can be used to select networks in certain geographic areas.
Another complicating factor has been mentioned briefly above, that is, analog versus digital operation. Systems can be either analog or digital communication systems. The PRL contains the indicators of whether a system is analog or digital. As described above with reference to PTT presence messages, some applications require digital systems, whereas some applications (such as many voice calls) can be on digital or analog systems.
If a device, such as D1 or D2 has acquired a system other than the most preferred system, known as a less preferred system or network, for its given geographic area, then the device is said to be roaming. When a device is roaming, it will scan for the most preferred system periodically, typically based on a scan timer. For example, if the device D1 has acquired a signal in network R1, then device D1 may scan for network H1 every 180 seconds. Or, for example, if the device D1 has acquired a signal in network R2, then device D1 may scan for both networks H1 and R1 every 180 seconds. The rescan time period can be any convenient time period, whether 180 seconds or not.
When a device has acquired a signal in a network, the device is said to be on, or in, that network, which can be called the present network. For convenience, when a device is on any network other than a most preferred network, it builds a scan list, as described above with respect to FIG. 5. The scan list is a subset of the PRL. The scan list includes all networks in the PRL that are more preferred than the present network and are in the same geographic area as the present network. When the scan timer expires, the device scans the scan list, which is faster than scanning the entire PRL.
However, scanning the scan list consumes resources in several ways. While the device is scanning for a more preferred network, it cannot receive or send communication on the present network. The result may include one or more of the following: (1) dropped pages; (2) missed voice calls; (3) missed SMS calls; (4) wasted network resources; and (5) battery life consumption resulting in talk time reduction or standby time reduction or both.
Scanning the scan list may take about one to five seconds. Typically, a scan list may include about one to five more preferred systems in the same geographical region. Typically, a wireless communication device might take about one second to scan for one system. Of course, these typical time estimates will change as scanning technology changes and as the number of systems increases or decreases. During the rescan the device is not available for communication. Thus, calls can be missed, among other things. This is aggravating to the user, such as S1 and S2, and results in lost revenue to the service provider.